Intermittent fasting: Does mental performance dip during food deprivation?

In a review of 71 global studies on food intake and cognition, researchers reassure that adults going without food for between about eight and 24 hours have no meaningful difference in mental performance.

However, children and adolescents tended to perform more poorly, reinforcing the importance of a proper breakfast before school.

“People often worry that if they fast, they won’t be able to concentrate at work or study effectively,” says senior author Dr. David Moreau, a neuroscientist at the University of Auckland, New Zealand.

“Our results show that, for most adults, short-term fasting is unlikely to have a major impact on mental sharpness.”

Nuanced findings

The study in Psychological Bulletin highlights that certain nuances, such as people performing worse in tests later in the day while fasting, suggest that the lack of food may amplify natural dips in the circadian rhythm. 

Tasks involving food-related cues, such as judging portion sizes or responding to images of food, seemed to impede performance. The authors suggest this might simply be because hungry individuals get distracted. 

“It seems the brain is quite resilient in the face of temporary food shortages,” says Moreau, who works in the University’s School of Psychology, leading the Brain Dynamics Lab.

“Humans evolved with periods of food scarcity, so it makes sense our cognitive systems can function well without constant refueling. That said, children and teenagers appear more vulnerable, which fits with what we know about their high energy demands.”

For most adults, short-term fasting is unlikely to have a major impact on mental sharpness.In the studies, the median fasting duration was 12 hours, and only a few participants extended their food restriction beyond 24 hours.

“These results don’t mean fasting is risk-free for everyone,” continues Moreau. “People with health conditions, children, and those fasting for extended periods may still experience negative effects. Our review highlights the need for careful consideration in these groups.”

Separate studies support the overall benefits of intermittent fasting in terms of metabolism. Recently, a paper in The BMJ revealed the protocol may outperform conventional calorie-restricted weight loss diets.

However, researchers also caution that without changing a person’s caloric intake, intermittent fasting does not lead to measurable improvements in metabolism or cardiovascular health.